I'm thinking of getting a small mtx amp http://www.crutchfield.com/S-SpA2SvJHzKK/cgi-bin/ProdView.asp?g=120&I=236TC3001 for my g35 and I will be connecting it with speaker level inputs. I don't want to change out the radio so I will use the speaker level inputs. My question is do you have to tap into both rear speakers or will one speaker +/- work for an input. Thanks